The present invention relates to an optical information recording and reading apparatus for recording and reading information into and out of an optical disk by means of a laser beam. More particularly, the present invention is concerned with an optical information recording and reading apparatus in which recorded information on the optical disk can be checked simultaneously with the recording in order to confirm whether the recording has been made correctly.
Generally, an optical information recording and reading apparatus employs an optical disk whose surface is coated by a photo-sensitive recording medium. The apparatus irradiates the optical disk with a tiny spot of laser beam for recording and reading information into and out of the medium. This type of apparatus can record information at a much higher density than the conventional apparatus such as magnetic disk apparatus. Accordingly, it can suitably be used as a recording apparatus having a large recording capacity. On the contrary, in this type of apparatus, mis-recording and mis-reading are often occurred due to the overly high density of recording of information.
More specifically, mis-recording is often caused by an insufficient irradiation of the laser beam and/or by a defect which may exist in the recording medium on the disk. In most optical disks presently utilized, recorded information cannot be erased and new information cannot be re-recorded thereon once the information is recorded on an vacant area of the medium. Therefore, it is quite important to confirm whether the recording has been made correctly because the area of the mis-recording should be invalidated and the mis-recorded information should be re-recorded in another area of the medium.
One of the conventional methods for confirming correct recording is to reproduce the information out of the optical disk after the recording process is completed in order to compare it with the original information. However, this method requires an additional step after recording for checking the recorded information.
Another method and a device for confirming correct recording are disclosed in the U.S. Pat. No. 4,145,758. This optical recording and reading apparatus has two optical systems for a recording laser beam and a reading laser beam, respectively. In this apparatus, a reading laser beam spot is positioned on the disk closely to the recording laser beam spot during recording the information so that the recorded information on the disk can be read immediately after the recording. Therefore, the recorded information on the disk can be checked substantially simultaneously with the recording. However, the reading laser beam spot is necessary to be precisely positioned on the same track to the recording laser beam spot. Accordingly, a control of two separate optical systems is extremely complicated.
The U.S. Pat. No. 4,308,612 discloses an optical recording apparatus which can perform the recording and an instantaneous check of the recorded information by means of a single laser beam applied to an optical disk. In this apparatus, the recorded information on the optical disk is checked by detecting a reflected beam of the recording laser beam reflected from the optical disk. When a pit is formed by the recording laser beam on the optical disk, the intensity level of the reflected beam is changed correspondingly. This apparatus compares the intensity level of the reflected beam with a predetermined reference level in order to confirm whether a pit corresponding to the information has been formed correctly. However, as a matter of fact, the intensitv of the recording laser beam applied to the optical disk is changed over a large amplitude range depending upon the information to be recorded (the intensity of the laser beam is high when a pit is to be formed and is low when a pit is not to be formed). Namely, the intensity of the reflected beam is also changed by a large amplitude in the same phase to the recording beam. Therefore, it is quite difficult to discriminate between the minor intensity change of the reflected beam corresponding to the pit formation and the major intensity change corresponding to the intensity change of the recording laser beam. In addition, since the period of intensity change of the recording laser beam is extremely short, extremely high operation speeds are required for a comparator circuit and a logical processing circuit to detect the intensity change of the reflected beam by comparing the reflected beam with the reference level. Further, since the intensity of the reflected beam tends to fluctuate in accordance with other factors, the reference level set in the comparator circuit has to be selected with a sufficient margin and accuracy in order to correctly detect the intensity change of the reflected beam due to the formation of the pit. Thus, in practice, this apparatus cannot accurately check the recorded information on the disk though it requires complicated device of high performance.